Yet another LM3886 heat sink question

[armstrom]

In anticipation of my LM3886 kit arriving I took a trip down to my local electronics surplus store (amazing place) to see what they have for heat sinks... I picked up a couple medium sized sinks  for $1.75 each. Think they will be large enough? They seem to be on the small side of what I have seen posted here. How about if I mount the chip to larger piece of copper plate and then mount two (or more?) of these heat sinks to the other side? Here are the dimensions:

4 1/2" L
2 3/8" W
7/8" Thick

16 fins.

Your thoughts?

[joecool85]

One is too small, but two or three (probably three, just to be safe) mounted to a piece of 1/4" or thicker copper would be fine.

[armstrom]

Great, thanks for the reply! At $1.75 each I really can't go wrong... There is another surplus store close by that sells bulk scrap copper plate. I'll find an appropriate size and go to town attaching heat sinks

On another note, has anyone found a suitable enclosure with integrated heat sink? Something along the lines of a car amp enclosure would be great (I think). Kill two birds with one stone.  Hammond sells one but the heat sink fins are along the top of the enclosure and it uses a t-slot for mounting (slip in a square nut and screw down the component) so applying thermal mastic would be tough.

http://www.hammondmfg.com/sinkbox.htm

-Matt

[nashvillebill]

...has anyone found a suitable enclosure with integrated heat sink? Something along the lines of a car amp enclosure would be great (I think). Kill two birds with one stone.  Hammond sells one but the heat sink fins are along the top of the enclosure and it uses a t-slot for mounting (slip in a square nut and screw down the component) so applying thermal mastic would be tough.

http://www.hammondmfg.com/sinkbox.htm

-Matt

Doesn't Parts Express have 'em?  www.partsexpress.com

[J M Fahey]

Dear Armstrom. I bolt my 100W poweramps (Tip141/142) to a 2mm aluminum backpanel and one heatsink, basically the same as yours, on its outer side. No thermal problems, at least on the last 15 or 20 years.  For a 70W chip such as yours, using your sink "alone", without any extra aluminum "help", probably will be be enough, if placed in a ventilated place (not inside a basically closed enclosure). Anyway joining 2 (or 3) sinks is not a bad idea at all, there´s not such a thing as "overheatsinking"

[armstrom]

Thanks for the reply. I have found another heatsink that is much larger than this one. I'm still not sure which route I'll go since I haven't decided on a cabinet for the amp yet.
-Matt

[joecool85]

Definetely go bigger rather than "might be big enough."  If you read through some of the threads here you will see that a few people have gone with heatsinks that "should be ok" and then fried their chip(s).  Plus big heat sinks look cool.

[armstrom]

Definetely go bigger rather than "might be big enough."  If you read through some of the threads here you will see that a few people have gone with heatsinks that "should be ok" and then fried their chip(s).  Plus big heat sinks look cool.

I will be trying to use the largest sink I can but I'm concerned about how I will fit everything into a cabinet. My plan is to create a combo amp with 2 10" or 12" speakers so trying to find room for a huge heat sink while still keeping a "normal" looking cabinet is proving to be difficult. Rack mount may be the easiest way to go but I'm building this amp for a friend to use for gigs so it's much easier to tote around a single cabinet than a head/cabinet combo.

Speaking of cabinets... what do you guys use? I've seen some amps built in salvaged cabinets but nearly everything else seems to be built as a head only inside either a nice rack mount chassis or a salvaged chassis from some other equipment  (VCRs, Hi-Fi amps, etc...) Does anyone build their own wood cabinets?
-Matt

[teemuk]

This one houses my "project amp's" chassis. It's only a head cabinet, though, but perhaps it can serve as one example. Timber came from an ugly old bookshelf and the black tweed-ish cloth was salvaged from an old sofa. (Speaking of sofas, right now I've been looking at few abandoned ones at the roadsides to be used as a source of leather-textured vinyl). The handle is a piece of an old leather belt. Making this cab cost me virtually nothing.

[armstrom]

looks great.  So do you normally house the amp electronics in a metal chassis and then somehow bolt that into whatever cabinet you're going to use (combination or just a head cabinet)? I suppose I need to do some searching for a metal chassis before I plan my cabinet I see a lot of people simply sticking boards down to the bottom of an old amp cab and I'm not sure thats the way to go for me. I could see maybe bolting the transformer down there since it's large and doesn't really need any RF shielding (at least compared to the inputs to the preamp that can tune radio stations if not properly shielded!).

Did you attach your heat sink to the metal chassis directly or is it attached to the wood of the cabinet? I was considering screwing the heat sink down to the wood and just cutting an aperture to allow the IC to bolt to the heat sink.

-Matt